On Aug. 1, the pair were seen kissing on the patio at West Hollywood’s Chateau Marmont — and after leaving, they spent the night together at John’s house, an insider reports. “It was obvious they’ve been seeing each other for a bit,” a source at Chateau Marmont says. “They seemed really comfortable together.”

Then on Aug. 4, they got cozy at a pool party in the Hollywood Hills. “John and Katy were all over each other,” an eyewitness at the party tells Star. “They were holding hands and kissing the entire time. Even in the pool, they stuck together nonstop.” After hanging out with friends there for a few hours, the two left hand in hand.

Katy, 27, clearly has a thing for bad boys. Her ex-husband, English comic Russell Brand, is a confessed former drug and sex addict. Since they split in December, she’s had flings with French model Baptiste Giabiconi and Florence + the Machine guitarist Robert Ackroyd. But her latest squeeze, John, may be the worst yet.

A confirmed womanizer, the Grammy-winning musician already has Katy head over heels. “Katy’s inner circle was anti-Russell and thought she’d learned her lesson about bad boys,” a friend says. “They flipped out after hearing she’s crazy about John — they think he’s far worse than Russell!”

FOR MORE ON KATY AND JOHN, PICK UP THE NEW ISSUE OF STAR, ON SALE NOW!